Single screw extruder

ABSTRACT

The invention relates to a single screw extruder comprising a barrier screw and a barrel in which the barrier screw is held in a manner that permits to rotate and comprising at least one feed zone longitudinal section and at least one melting zone longitudinal section ( 23 ). The extruder ( 10 ) is characterized in that the barrel ( 11 ), on the inner wall ( 50 ) thereof in the area of the melting zone longitudinal section ( 23 ), has at least one groove ( 52 ) which runs in a longitudinal direction. The invention also relates to a method for extruding plastic material using a single screw extruder ( 10 ) comprising a barrier screw ( 40 ) which is held inside a cylinder ( 11 ) in a manner that permits it to rotate, whereby the extruder ( 10 ) comprises a feed zone ( 21, 22 ) and a melting zone ( 23 ), and the barrier screw ( 40 ) has at least one solid matter channel ( 49 ) and a melting channel ( 48 ). The method is characterized in that solid plastic material (solid matter) is transported in the area of the melting zone ( 23 ) in a defined quantity out of the solid matter channel ( 49 ) and into the melt channel ( 48 ).

CROSSREFERENCES TO RELATED APPLICATIONS

[0001] This Application is a continuation of international patentapplication PCT/EP00/05919 filed on Jun. 6, 2000 and designating U.S.,which claims priority of German patent application DE 199 28 870.4 filedon Jun. 24, 1999.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to a single screw extrudercomprising a barrier screw and a barrel in which the barrier screw isrotatably mounted and which comprises at least a feed zone longitudinalsection and a melting zone longitudinal section. The invention furtherrelates to a method for extruding plastic material using such a singlescrew extruder.

[0003] A single screw extruder having a barrier screw is for exampledisclosed in the paper “Zylinder glatt oder genutet”, Maschinenmarkt,Würzburg 95 (1989) 48, pages 40-43. In this paper different concepts ofbarrier screws are presented which are used in extruders having smoothor grooved feed areas. The barrels in the area of the melting zonelongitudinal sections are formed in a plane and smooth manner for abetter separation of melt and solid matter.

[0004] A screw housing for an extruder is known from DE 25 14 307, whichcomprises at least one groove extending across the whole length. Thisgroove serves to avoid a “screw slip”, that is a rotation of the screwwithout a transport of material in the barrel. The screw shown in thisdocument is not a barrier screw.

[0005] Generally single screw extruders are known. They typicallycomprise an extruder plastification barrel in which a screw is rotatablymounted. A powdered or granulated initial material (with stabilizers,slip additives, if required thermoplastic materials being added withfillers and colorings) is fed at one end of the barrel and istransported by the rotating screw through the barrel to a so-calleddemoulding tool or matrix located at the opposite end. At first, theinitial material is conveyed or transported through the so-called feedzone and is thereby compressed. This feed zone is followed by a meltingzone and plastification zone, respectively, in which the initialmaterial is melted by friction at the barrel inner surface. The meltingprocess may—particularly when starting the extruder—be supported by anouter heating of the barrel via (mostly electrical) heating elements.Depending on the application the melting zone is followed by ahomogenizing zone and a demoulding zone in which the plastified materialis prepared for further processing.

[0006] In recent years, single screw extruders being based on theso-called barrier screw concept have gained acceptance to an increasingextent. In a so-called barrier screw, the screw channel is divided in asolid matter channel and a melt channel by way of a further side bar.Compared with the primary side bar, being known from conventionalscrews, the smaller formed barrier side bar allows a transverse flow ofmelt from the solid matter channel into the melt channel. Thecross-section of the melt channel increases in a downstream directionwhereas the cross-section of the solid matter channel continuouslydecreases in the downstream direction as to maintain the desiredconveying effect of the screw. Due to the so-called barrier zoneparticularly the heat transfer from the barrel and the screw surface tothe granulate not yet melted is improved.

[0007] Although this barrier screw concept has been proven practical formany applications still remains it the need to increase the performanceof the single screw extruder with barrier screw while keeping thenecessary structural measures as low as possible.

SUMMARY OF THE INVENTION

[0008] The object of the present invention is, therefore, to improve thesingle screw extruder based on the barrier screw concept so that theperformance, particularly the output and the pressure build-upcapability as well as the melting performance, is increased.

[0009] The object underlying the present invention is solved by a singlescrew extruder of the aforementioned kind in that the barrel comprisesat least one groove extending in a longitudinal direction and formed inthe barrel's inner surface in the area of the melting zone longitudinalsection.

[0010] By way of combining a barrier screw with a barrel comprising atleast one groove along the melting zone, a substantial increase ofoutput compared to conventional barrier screw extruders is achievable.This is particularly the result of an improvement of the melting processof the initial material. This may substantially be put down to the factthat the solid matter gets caught in the groove and, therefore, entersthe melt channel only in small quantities. This also leads to theadvantage that the heat transfer is substantially improved since thebarrel surface in the area of the grooves comes in contact with thesolid matter. In the prior known barrels with a smooth surface the meltquasi forms a heat barrier, at least said smooth surface made worse theheat transfer from the barrel surface to the inside.

[0011] The mentioned improvement of the melting process and the heattransfer allows to increase the rotational speed directed output withouthaving to provide additional structural measures. In view of the priorsingle screw extruders it was necessary for increasing the output toincrease the length of the melting zone and/or the rotational speed ofthe screw. However, an increased rotational speed results in anundesired heating process of the melt in the extruder which may causedamages of the initial material. Otherwise the melt must be more cooleddown afterwards which in turn results in additional structural measures.

[0012] Additional structural measures are therefore not necessary withthe single screw extruder according to the present invention. The objectof the present invention is hence completely solved.

[0013] In addition to the aforementioned advantages the single screwextruder with barrier screw according to the present invention has theadvantage that the pressure build-up capability is improved. Compared tothe known single screw extruders it is not necessary any more to buildup a very high pressure in the so-called feed zone as to enable apredetermined lower pressure at the end of the single screw extruder.With the single screw extruder according to the present invention it ispossible to substantially reduce the pressure between the feed zone andthe melting zone. This in turn results in a reduction of wear of thescrew in the transition area between the feed zone and the melting zonesince it is operated with lower pressures.

[0014] Due to the pressure reduction in the area of the feed zone itdoes not have to be constructed any more as complicated as in priorsolutions and does not have to be provided with cooling means and a“heat separation” towards the heated melting zone. Advantageously, thefeed zone and the melting zone may therefore be formed individually.

[0015] In a preferred embodiment of the present invention the grooveextends parallel to the longitudinal axis of the barrel (axial groove),wherein more preferably the grooves extend helically in the feed zone.

[0016] It has been shown that the axially extending form of the grooveprovides optimal results particularly in view of the output and thepressure build-up, however, without deteriorating the melting processand the homogeneity of the melt, respectively. Of course, a helicallyarranged groove may also be contemplated.

[0017] In a preferred embodiment the barrel comprises several groovesbeing equally spaced apart in circumferential direction which groovesextend preferably parallel to the longitudinal axis of the barrel.

[0018] This has the advantage that the process of matching the groovesis simplified compared with the groove helically arranged.

[0019] In a further preferred embodiment the width and/or the depth ofthe groove varies in a longitudinal direction, preferably the groovesdepth decreases towards the downstream end of the melting zone section,preferably to zero.

[0020] In a further preferred embodiment of the invention at least onegroove is provided also in the barrel inner surface (innerwall) in thearea of the feed zone section, the groove extending parallel orhelically relative to the longitudinal axis. Preferably, the groove inthe area of the feed zone section leads into the groove in the area ofthe melting zone without transition. Preferably both grooves have thesame lead angle.

[0021] This has the advantage that the groove extends continuouslywithout any break along the feed zone and melting zone thereby furtherimproving the output and the pressure build-up.

[0022] In a preferred embodiment the barrel is formed as a one-piecebarrel and is preferably provided with a constant inner diameter. Thismeasure has the advantage that the conventional and structurallycomplicated separation into a feed zone with a cooled grooved liner anda heated melting zone may be omitted. Thereby manufacturing costs may besaved. Moreover, due to the good output of the overall system a coolingof the feed zone may be omitted which leads to operation cost savings.

[0023] In a further preferred embodiment the barrier screw is formedwith two or more channel pairs so that two or more solid matter channelsand two or more melt channels are created.

[0024] This has the advantage that the melting performance of the singlescrew extruder may be improved compared with the one channel pairedbarrier screw. Additionally, the abrasive wear at the primary side barof the screw may be minimized thereby.

[0025] The object underlying the present invention is also solved by amethod of the aforementioned kind which is characterized in that in thearea of the melting zone solid plastic material (solid matter) istransported in a defined quantity out of the solid matter channel intothe melt channel. Preferably, the solid matter is transported out of thesolid matter channel into the melt channel at predetermined locationsalong the barrel. Most preferred, the transport of the predeterminedquantity of solid matter is caused by the pressure difference betweenthe solid matter channel and the melt channel.

[0026] Further advantages and embodiments of the invention will beapparent from the following description and the drawings.

[0027] It is understood that the features recited above and those yet tobe explained below can be used not only in the respective combinationindicated, but also in other combinations or in isolation withoutleaving the context of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The invention will now be explained with one embodiment and withreference to the drawings. In the drawings:

[0029]FIG. 1a schematically shows a cross-sectional view of a singlescrew extruder according to a first embodiment;

[0030]FIG. 1b schematically shows a cross-sectional view of a portion ofa single screw extruder according to a second embodiment;

[0031]FIG. 2 is a diagram of a barrier screw;

[0032]FIG. 3 is a diagram of a longitudinal section of the extruder inthe area of the melting zone;

[0033]FIG. 4a is a diagram of a cross-section of the barrier screw in atwo-channel design; and

[0034]FIG. 4b is a diagram of a portion of the inner surface of thebarrel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] In FIG. 1a, a single screw extruder for extruding a plasticmaterial is designated with reference numeral 10. The single screwextruder 10 (hereinafter simply called extruder) comprises a tubularbarrel 11 which is made up of three single tubular barrel assemblies 12,14, 16 in the present embodiment. The connection of the singleassemblies 12, 14, 16 is achieved by respective flanges 17.

[0036] The barrel 11 is divided in multiple functional longitudinalsections, namely a filling zone 21 followed by a feed zone 22, a meltingzone 23, a homogenizing zone 24 and finally a demoulding zone 25. InFIG. 1a, the filling zone 21 forms the right end and the demoulding zone25 forms the left end of the barrel 11.

[0037] Within the barrel 11, a screw 30 is coaxially and rotatablymounted therein. For clarity reasons neither the screw drive nor thescrew bearings are shown. Moreover, for clarity reasons the diagram doesalso not show that the screw according to the present invention isformed as a barrier screw. A more detailed description of the barrierscrew follows hereinafter. The screw 30 extends from the screw shaft andthe filling zone 21 to the end of the homogenizing zone 24. In theassembly 12 of the barrel 11 an opening 27 is provided in the area ofthe filling zone 21, the opening allowing a connection from outside intothe inner space of the barrel 11. For improving the feeding of initialmaterial a funnel 28 is mounted on the opening 27.

[0038]FIG. 1a further shows that the assembly 12 comprises an innerliner 32 which is inserted into the tubular assembly 12. The liner 32comprises axial grooves formed at its surface facing the screw 30. InFIG. 1a, two of these grooves are designated with reference numeral 33.Typically, the liner 32 comprises a plurality of axial grooves equallyspaced apart to each other in a circumferential direction. The depth ofthe grooves 33 in the area of the fill zone 21 is at a maximum andgenerally decreases continuously in the transport direction. At the endof the feed zone 22 the groove depth is generally zero.

[0039] The liner 32 is surrounded by ring shaped or helically shapedcooling channels 35, neither the coolant input nor the coolant outputbeing shown for clarity reasons.

[0040] The tubular barrel assembly 14 is surrounded by schematicallyillustrated heating elements 38, the heating elements 38 extendingacross the whole length of the assembly so that both the melting zone 23and the homogenizing zone 24 are heatable by these heating elements 38.In the aforementioned embodiment multiple heating elements 38 arearranged one behind the other in longitudinal direction. A furtherheating element 38 also surrounds the third assembly 16 in the area ofthe demoulding zone 25. The heating element could also be provided withcooling elements as to reject surplus friction heat caused by a higherrotational speed of the screw.

[0041] In the embodiment of the extruder 10 shown in FIG. 1a, bothassemblies 12 and 14 are connected with each other via a flange 17. Itis of course also possible to integrate both assemblies 12, 14 into oneassembly 13 so that a flange connection could be avoided. Thisembodiment of an extruder 10′ which is improved in view of structuralefforts is also shown in FIG. 1b as a partial view. Beside the integralform of the assembly 13 it can be seen that neither a grooved liner 32nor a cooling in form of cooling channels 35 are provided. The portionsof the extruder 10′ not shown, however, correspond to that of extruder10 of FIG. 1a. Further, in both FIGS. 1a, 1 b alike parts are designatedwith alike reference numerals so that it can be refrained fromdescribing these parts again.

[0042] Such an extruder 10 and 10′, respectively, generally performs thefollowing functions:

[0043] A mostly granulated initial material made of plastic is fed intothe funnel 28, which then passes the opening 27 and enters the fillingzone 28. By rotating the screw 30 this initial material is transported(conveyed)—in FIG. 1 to the left-hand side. By a respective design ofthe screw 30 and the grooves 33 the initial material is compressed inthe feed zone 22. Due to the pressure build-up which is supported by thegrooves 32 a cooling of this portion via the cooling channels 35 isnecessary. After having passed the feed zone 22 the compressed initialmaterial (solid matter) enters the melting zone 23 in which a melting ofthe solid matter occurs by friction of the solid matter at the barrelinner surface and/or by heating via the heating elements 38. At the endof the melting zone 23 the melt enters the homogenizing zone 24 in whichthe correspondingly formed screw 30 performs a melting of solid matteryet present. Further, in this zone additives may be mixed effectively.The homogenized melt finally enters the demoulding zone 25 where themelt is prepared for further processing.

[0044] The output of the extruder 10 substantially depends on therotational speed of the screw 30. A desired increase of the output couldtherefore be achieved by increasing the rotational speed. However, thenthe problem arises that the degree of homogeneity of the melt at the endof the melting zone 23 deteriorates because many solid matter particleshave passed the melting zone 23 too fast. Moreover, the melt filmcreated at the barrel inner surface acts like a heat insulator whichprevents an effective heat transfer from the heat/cooling elements 38 tothe solid matter.

[0045] An improvement of performance compared to a conventional screw isprovided by a so-called barrier screw, which is schematicallyillustrated in FIG. 2 and which is designated as screw 30 in theextruder 10 of FIG. 1a. The barrier screw as such is known so that adescription of the detailed structure and function can be avoided. Adescription of the function of such a barrier screw is, for example,disclosed in “Der Einschnecken-Extruder—Grundlagen undSystemoptimierung”, VDI-Verlag 1997.

[0046] In FIG. 2, a barrier screw is designated with the referencenumeral 40. The barrier screw 40 comprises multiple longitudinalsections, only the longitudinal section designated with referencenumeral 42 being of importance for the following description. Thislongitudinal section 42 is located within the melting zone 23 of thebarrel 11 in the built-in condition. The barrier screw 40 ischaracterized in that it comprises a so-called barrier side bar 46beside the primary or main side bar 44.

[0047] The primary side bar 44 and the barrier side bar 46 following indownstream direction form together a melt channel 48 and the primaryside bar 44 and the barrier side bar 46 following in upstream directionform together a solid matter channel 49. FIG. 2 yet shows that the widthof the solid matter channel decreases towards the downstream end of thelongitudinal section 42, whereas the width of the melt channel 48increases. The particular function of the barrier screw 40 is amongother things based on the fact that the gap between the barrel innersurface and the primary side bar is smaller than the gap between thebarrier side bar 46 and the barrel inner surface. This may be especiallyseen in FIG. 4a in which a barrier screw having two channel pairs isillustrated as a sectional view. In FIG. 4a both diametrically opposedprimary side bars 44 and both also diametrically opposed barrier sidebars 46 can be clearly seen. In FIG. 4a, the gap between the primaryside bar 44 and the inner surface 50 of the barrel 11 (blocking gap) isdesignated with δ_(s) and the gap between the barrier side bar 46 andthe inner surface 50 (barrier gap) with δ_(ü).

[0048] In barrier screws δ_(s) is generally smaller than δ_(ü). Asalready mentioned the solid matter channel is formed between a barrierside bar 46 and a primary side bar 44—when seen in conveyingdirection—and the melt channel 48 is formed between the primary side bar44 and the following barrier side bar 46. Two of such solid matterchannels 49 and two melt channels 48 are provided in the two channelpaired embodiment shown herein.

[0049] According to the present invention grooves 52 are formed in theinner surface 50 of the barrel 11 in the area of the melting zone 23. Inthe present embodiment shown in FIG. 4a a total of eight grooves 52 areprovided which extend in axial direction and which are equally spacedapart to each other in a circumferential direction of the barrel.Further, the grooves have a rectangular cross-section. However, it isparticularly advantageous to provide the grooves 52 such that no sharpedges are created. Merely as an example, a single groove 52′ havingrounded edges is shown in FIG. 4a. It is of course also possible andadvantageous to provide one or a plurality of helically arranged grooves52′ as illustrated in FIG. 4b, instead of a plurality of axial grooves52.

[0050] The grooves 52 have a depth which may be substantially in thesame order as the width of the primary side bar 44 and the barrier sidebar 46, respectively. The depth of the grooves 52 has to be selecteddependent on the application and it must be paid attention that thedepth is not selected too large since otherwise a deterioration of thefunction is expected. Both the groove depth as well as the groove widthcan vary in a longitudinal direction of the barrel 11 and the groovedepth runs substantially to zero preferably in the downstream end areaof the melting zone 23. This tapered end of the grooves 52 has beenproven as particularly advantageous.

[0051] In FIG. 3, a longitudinal section of the barrel 11 in the area ofthe melting zone 23 is again schematically illustrated. The barrierscrew 40 comprises two helically extending primary side bars 44 and tworespectively spaced apart also helically extending barrier side bars 46.As already mentioned, a primary side bar 44 and a barrier side bar 46each restricts the melt channel 48 and the solid matter channel 49,respectively. In FIG. 3, a total of three grooves 52 can be seen eachhaving a groove depth h_(N).

[0052] The grooves 52 may be formed differently in the area of themelting zone 23 than in the area of the feed and solid matter zone 21,22. As to achieve very small solid matter particles a relatively highnumber of narrow flat helically or axially extending grooves can beprovide in the barrel's inner surface of the melting zone 23. Thisresults in an increase of the effective heat transfer area resulting inan improvement of the melting process.

[0053] In operation of the barrier screw 40 in the barrel section 23provided with grooves 52, the following occurs:

[0054] The screw section in the feed zone 22 presses the solid matterinto the solid matter channel 49 of the barrier screw 40 in the meltingzone 23. The solid matter is hence pressurized in the solid matterchannel 49 and in case of the desired high output, the pressure isgenerally higher than the pressure in the melt channel 48. Due to thepressure difference between the solid matter channel 49 and the meltchannel 48 the solid matter tries to enter the melt channel 48. Due tothe selected gaps between the side bar 46, 44 and the inner surface 50only the melted solid matter enters the melt channel 48 as melt passingthe barrier side bar 46. The gap between the primary side bar 44 and theinner surface 50 is too small also for melt. Because according to thepresent invention grooves 52 are provided in the inner surface 50 of thebarrel 11, the gap between the inner surface and the primary side bar 44and the barrier side bar 46, respectively, increases every time therespective side bar passes the groove 52. This has the result that thesolid matter pressed into the groove 52 enters the melt channel 48 insmall quantities. For example, in FIG. 3 it is indicated with A, thatsolid matter is pressed into the groove 52 displacing the melt in thegroove therewith. This displaced melt flows into the melt channel 48what is indicated with B. Additionally the mixture of solid matter andmelt in the grooves 52 is pressed into the melt channel 48, as indicatedby C. These “small doses” of solid matter are more or less melted in themelt channel 48. Inhomogeneities which will probably be there at the endof the melting zone 23, are eliminated in the following homogenizingzone 24. However, this passing-over of solid matter leads to the resultthat the pressure in the solid matter channel can be reducedsignificantly with the result that also the abrasive wear of the screw30 and the barrel 11 can be reduced.

[0055] Because the solid matter enters the melt channel 48 in smalldefined quantities in an early stage, an early mixture of melt and smallsolid matter particles can be performed so that on the one hand theresulting melt temperature can be kept on a low level also at a highrotational speed in an advantageous manner and on the other hand thehomogeneity of the melt can be ensured.

[0056] As mentioned above, the barrier gap is generally greater than theblocking gap. However, it is also possible that the barrier gap isgreater than or equal to the blocking gap. In a production-oriented verysimple embodiment the barrier gap can be equal to the blocking gap whichprevents a separate grinding of the barrier side bars. Preferably thegap width is selected a little bit greater compared with conventionalextruder screws so that the overpressing of melt and solid matterparticles is not impeded. Therewith, the resulting melt temperature canalso be reduced in an advantageous manner.

[0057] The overpressing of melt and small solid matter particles can bemade easier preferably by small slots in the barrier side bar and/or theprimary side bar, which can extend substantially radially and in acircumferential direction. Although the production-oriented effort issomewhat higher, the possible output, however, is increased and the melthomogeneity and the melt temperature is improved, respectively.

[0058] In view of this the grooves according to the present inventionprovided in the barrel inner surface prevent a deterioration of thehomogeneity and the heat transfer in case that the output is increased.The rotational speed of the screw can therefore be increased withoutadditional structural measures, as e.g. an extension of the meltingzone, an increase of the measures for heating or cooling the barrel.Further, it has been proved that the grooves show the aforementionedeffects particularly in extruders having a barrier screw.

What is claimed is:
 1. Single screw extruder with a barrier screw and abarrel in which the barrier screw is rotatably mounted and whichcomprises at least a feed zone longitudinal section and a melting zonelongitudinal section, wherein the barrel comprises at its inner surfaceat least one groove extending in a longitudinal direction in the area ofthe melting zone longitudinal section.
 2. Single screw extruderaccording to claim 1, wherein the groove extends parallel to thelongitudinal axis of the barrel.
 3. Single screw extruder according toclaim 2, wherein the grooves provided in the feed zone longitudinalsection extend helically.
 4. Single screw extruder according to claim 1,wherein a plurality of grooves spaced apart in a circumferentialdirection of the barrel are provided.
 5. Single screw extruder accordingto claim 1, wherein the width and/or depth (h_(N)) of the groove(s) varyin the longitudinal direction.
 6. Single screw extruder according toclaim 5, wherein the depth (h_(N)) of the groove decreases towards thedownstream end of the melting zone section preferably to zero.
 7. Singlescrew extruder according to claim 1, wherein at least one groove isprovided in the barrel inner surface in the area of the feed zonesection, the groove extending parallel or helically relative to thelongitudinal axis.
 8. Single screw extruder according to claim 7,wherein the groove in the area of the feed zone section leads directlyinto the groove in the area of the melting zone.
 9. Single screwextruder according to claim 8, wherein both grooves have the same leadangle.
 10. Single screw extruder according to claim 1, wherein the leadangle of the groove is variably formed along the longitudinal axis. 11.Single screw extruder according to claim 1, wherein the barrel isprovided as a one-piece barrel.
 12. Single screw extruder according toclaim 11, wherein the melting zone section is provided as a barrel tubeand the feed zone section is provided as a grooved liner.
 13. Singlescrew extruder according to claim 1, wherein the barrel has an innerspace with a diameter being constant in longitudinal direction. 14.Single screw extruder according to claim 1, wherein the barrier screw isprovided with two or more channel pairs so that two or more solid matterchannels and two or more melt channels are defined.
 15. Single screwextruder according to claim 1, wherein the barrier screw comprises aprimary side bar and a barrier side bar which defines together with abarrel inner surface in the area of the melting zone longitudinalsection respective gaps, both gaps being equal.
 16. Single screwextruder according to claim 1, the barrier screw comprising a primaryside bar and a barrier side bar, wherein slots are provided in theprimary side bar and/or the barrier side bar, the slots extending in asubstantially radial and circumferential direction.
 17. Single screwextruder according to claim 1, wherein the groove in the melting zonelongitudinal section is formed differently to the grooves in the feedzone longitudinal section.
 18. Single screw extruder according to claim17, wherein a great number of narrow and flat helically or axiallyextending grooves are provided.
 19. Method for extruding plasticmaterial using a single screw extruder which comprises a barrel and abarrier screw rotatably mounted therein, the extruder comprising a feedzone and a melting zone and the barrier screw comprising at least asolid matter channel and a melt channel, wherein in the area of themelting zone solid plastic material (solid matter) is transported fromthe solid matter channel to the melt channel in defined quantities. 20.Method according to claim 19, wherein the solid matter is transported atdefined locations along the barrel from the solid matter channel intothe melt channel.
 21. Method according to claim 19, wherein thetransport of defined quantities of solid matter is substantially causedby the pressure difference between the solid matter channel and the meltchannel.